The present invention relates to a holder assembly for an abrasive (including polishing) disc. More specifically the invention relates to a holder which allows for a quick manual change of the abrasive disc.
Abrasive articles generally contain an abrasive material, typically in the form of abrasive grains, abrasive brushes or nonwoven abrasive filaments bonded to a backing plate. Such articles usually take the form of sheets, discs, belts, bands, and the like, which can be adapted to be mounted on power tools. A variety of abrasive articles are used to abrade or polish various substrates, including steel and other metals, wood, wood-like laminates, plastic, fiberglass, leather, and ceramics. The abrasive articles can be in any of a variety of forms, including coated abrasives, bounded abrasives, abrasive brushes, and nonwoven abrasives. Such articles ususally take the form of sheets, discs, belts, bands, and the like, which may be adapted, for example, to be mounted on pulleys, wheels, or drums.
Many abrasive articles are used as discs in grinding assemblies. A typical such abrasive sanding or grinding assembly includes: an annular back-up pad made from a resilient and reinforced material such as rubber or plastic and an abrasive disc having a backing plate and an abrasive material (e.g., coated abrasive discs and nonwoven abrasive discs that include abrasive materials such as abrasive grains). The abrasive material may completely or partially cover the surface of the backing plate. For example, one type of abrasive disc uses a thick annular ring of abrasive material applied to the backing plate such that the inner radial boundary of the abrasive is concentric with the backing plate. Examples of abrasive discs having an annulus of abrasive material include flap discs, non-woven surface conditioning discs, and grinding wheels. The backing plate used in the abrasive discs are typically made of paper, certain polymeric materials (e.g., phenolic impregnated fiberglass), cloth, nonwoven materials, vulcanized fiber, and combinations of these materials. During the grinding process, the disc may be subjected to relatively severe stresses.
Abrasive discs have a finite useful life when applied against a workpiece. The discs are disposable so that they can be replaced after use. It is highly desirable for the discs to be easily and quickly removed and replaced.
In the past, many methods have been used to secure the abrasive disc to the tool. For example, it is known to mechanically mount a hub on the back side of the disc, the hub being attachable to the end of a tool shaft. If the torque load is substantial, the disc tends to rupture at the periphery of the hub or to separate from the hub. In addition to such disadvantages, a suitable hub and its permanent mounting on the disc involves a significant cost factor, as it must be discarded with the used disc.
An improvement includes attaching an abrasive disc to a tool by way of a holder assembly. Holders commonly include a back up pad or plate that supports the abrasive disc during use, thereby allowing an operator to exert frictional pressure on a workpiece. When the holder is rotated, the disc rotates with it, permitting the moving disc surface to effectively finish the surface of workpieces such as furniture and automobile body parts.
A variety of holder structures have been used heretofore to secure the abrasive disc to the power tool. One of the most common types includes a support pad having a reinforced central aperture arranged to be engaged over the threaded end of the rotary shaft of the power tool. The abrasive disc is placed on the flat surface of the pad and a flanged nut is turned down onto the shaft end protruding through both the holder and the disc. When the nut is tightened, it lays flush against the abrasive surface of the disc and clamps the disc to the support pad. In use, the shaft of the assembly is rotated and the abrasive surface of the disc is pressed against a workpiece with considerable force, abrading the workpiece.
During use of the abrasive disc, torque forces cause the nut member to lock onto the shaft with greater and greater holding force. Therefore, with conventional devices, the abrasive disc member can become locked so tightly onto the holder that it is difficult to remove and replace the abrasive disc. In many heavy industrial applications, the discs must be replaced quite often (e.g., over five times per hour). Consequently, considering the number of tools in use on a given shift, such disc replacement necessitates an excessive amount of downtime.
Several attempts have been made to address the problem of tightly locked discs on holders (see, e.g., U.S. Pat. No. 3,765,130 (Block), U.S. Pat. No. 4,439,953 (Block et al.), U.S. Pat. No. 4,637,170 (Block), U.S. Pat. No. 4,655,006 (Block), and U.S. Pat. No. 4,683,683 (Block)). Disadvantages of such solutions typically include one or more of the following; for example, in some of these designs, because the abrasive disc and back up assembly are very close in both size and position, it is very difficult to grasp just the abrasive disc and turn it relative to the back up assembly for removal. In others, a disc or disc fastener must be especially designed for use with the particular back up assembly, rather than of a universal design to fit the threaded rotating shaft of a tool.
In one aspect, the present invention provides a holder for supporting an abrasive disc on a tool shaft. The holder comprises an annular internally threaded central insert threadably engaging the shaft; a handle concentrically surrounding and in fixed rotational engagement with the central insert; a hub concentrically surrounding the central insert, abutting the handle, and rotationally engaged to the handle; a pin disposed on a first face; a discontinuous channel disposed on a second face, the channel opposing the pin, so that the pin engages the channel and travels within the channel as the handle and hub are rotated with respect to each other; and a faceplate concentrically surrounding the central insert, abutting the hub, and removably engaged to the hub. In a preferred embodiment, the first face is disposed on the handle, and the second face is disposed on the hub.
The invention can be used with most standard abrasive discs which are designed to thread directly onto a tool shaft. Its design allows a user to easily grasp the handle and counterrotate it with respect to the hub, faceplate, and abrasive disc, to loosen the abrasive disc from the tool shaft.